Two mammalian bradykinin receptor subtypes, B.sub.1 and B.sub.2, have been defined based on their pharmacological properties (A. Dray, M. Perkins, TINS 16, 99-104 (1993), D. Proud, A. P. Kaplan, Annual Review Immunology 6, 49-83 (1988)). The nonapeptide bradykinin (BK) and the decapeptide Lys-BK (kallidin) are liberated from the large protein precursor kininogen by the proteolytic action of kallikreins. Because of their rapid degradation, these peptide hormones are presumed to mediate local effects. BK and kallidin both activate the B.sub.2 receptor. These B.sub.2 receptor agonists are then degraded by a carboxypeptidase to produce the B.sub.1 receptor agonists des-Arg.sup.9 BK and des-Arg.sup.10 kallidin or by the angiotensin converting enzyme (ACE) to yield inactive peptides. The phenomenon of the proteolytic transformation of a compound from B.sub.2 to B.sub.1 selectivity has been observed not only for the endogenous kinin agonists but also for several synthetic peptide antagonists (K. Wirth, et al., European Journal of Pharmacology 205, 217-218 (1991), D. Regoli, et al., European Journal of Pharmacology 127, 219-224 (1986)). BK and kallidin act as equipotent agonists at the B.sub.2 bradykinin receptor subtype. In contrast, BK is totally inactive at the B.sub.1 bradykinin receptor subtype. Although traditionally des-Arg.sup.9 BK has been utilized to study the B.sub.1 receptor, the most potent agonist for the B.sub.1 receptor appears to be des-Arg.sup.10 kallidin (D. Regoli, et al., European Journal of Pharmacology 127, 219-224 (1986)).
Bradykinin and kallidin, acting through the B.sub.2 receptor present in smooth muscle and certain neurons, cause pronounced hypotension and are potent mediators of pain and inflammation (A. Dray, supra; D. Proud, supra). In contrast, the B.sub.1 receptor is not detected in most normal tissues and appears to act predominantly in pathophysiological conditions (A. Dray, supra). The B.sub.1 receptor was originally discovered through a contractile response to des-Arg.sup.9 BK that was observed in rabbit aortic strips only after a prolonged ex vivo incubation (D. Regoli, J. Barabe, W. K. Park, Canadian Journal of Physiology and Pharmacology 55, 855-867 (1977); D. Regoli, F. Marceau, J. Barabe, Canadian Journal of Physiology and Pharmacology 56, 674-677 (1978); D. Regoli, J. Barabe, Pharmacological Reviews 32, 1-46 (1980)). The de novo synthesis of B.sub.1 receptors has been reported in vivo following treatment with bacterial lipopolysaccharide (LPS) (D. C. Regoli, R. Marceau, J. Lavigne, European Journal of Pharmacology 71, 105-115 (1981)), and in animal models of antigen arthritis (S. G. Farmer, B. A. McMillan, S. N. Meeker, R. M. Burch, Agents and Action 34, 191-193 (1991)). In vitro studies have implicated a number of cytokines, most notably interleukin-1 (IL-1) and IL-2, as mediators that induce the expression of B.sub.1 receptors (D. Regoli, supra; D. Deblois, J. Bouthillier, F. Marceau, British Journal of Pharmacology 93, 969-977 (1988); D. deBlois, J. Bouthillier, F. Marceau, British Journal of Pharmacology 103, 1057-1066 (1991); D. deBlois, J. Bouthillier, R. Marceau, Immunopharmacology 17, 187-198 (1989)). These results, in conjunction with the finding that activation of a B.sub.1 bradykinin receptor on mouse macrophages causes the release of cytokines (R. M. Burch, J. R. Connor, C. W. Tiffany, Agents and Action 27, 258-260 (1989); C. W. Tiffany, R. M. Burch, FEBS letters 247, 189-192 (1989)), suggest that the B.sub.1 receptor could be an important mediator of chronic inflammation. Significantly, the B.sub.1 bradykinin receptor antagonist des-Arg.sup.9 [Leu.sup.8 ]BK was recently found to alleviate hyperalgesia in animal models of persistent inflammation (A. Dray, supra; M. N. Perkins, D. Kelly, British Journal of Pharmacology 110, 1441-1444 (1993); M. N. Perkins, E. Campbell, A. Dray, Pain 53, 191-197 (1993)). Thus, a body of evidence implicates the B.sub.1 bradykinin receptor in the pathophysiology of inflammation. Relatively little is known about the role for the B.sub.1 receptor in healthy tissues, although both B.sub.1 and B.sub.2 receptors may play a physiological role in renal function (N.-E. Rhaleb, et al., European Journal of Pharmacology 162,419-427 (1989); M. Lortie, D. Regoli, N.-E. Rhaleb, G. E. Plante, American Journal of Physiology 262, R72-R76 (1992)). The apparent inducibility of the B.sub.1 receptor under pathological conditions may provide a therapeutic window for the use of B.sub.1 receptor antagonists in treating chronic inflammation.
The cloning of the B.sub.2 bradykinin receptor revealed that this receptor is a member of the superfamily of G-protein coupled receptors (A. E. McEachem, et al., Proc. Natl. Acad. Sci. 88, 7724-7728 (1991); S. J. Powell, et al., Genomics 15, 435-438 (1993); J. F. Hess, J. A. Borkowski, G. S. Young, C. D. Strader, R. W. Ransom, Biochem. and Biophys. Res. Comm. 184, 260-268 (1992); D. Eggerickx, E. Raspe, D. Bertrand, G. Vassart, M. Parmentier, Biochem. Biophys. Res. Comm. 187, 1306-1313 (1992)). The rat B.sub.2 bradykinin receptor was cloned using a Xenopus oocyte expression system (A. E. McEachern, et al., supra) that exploited the ability of the B.sub.2 receptor to act through G-proteins to activate phospholipase C and mobilize Ca.sup.2+ (R. M. Burch, J. Axelrod, Proc. Natl. Acad. Sci. 84, 6374-6378 (1987); S. R. Slivka, P. A. Insel, J. Biol. Chem 263, 14640-14647 (1988)). Recently, the B.sub.1 bradykinin receptor in rabbit aorta and rat mesangial cultured cells has also been shown to activate phospholipase C leading to Ca.sup.2+ mobilization (K. A. Schneck, supra; M. Issandou, J.-M. Darbon, Journal of Biological Chemistry 259, 9263-9268 (1991); M. M. Tropea, D. Gummelt, M. S. Herzig, L. M. F. Leeb-Lundberg, Journal of Pharmacology and Experimental Therapeutics 264, 930-937 (1993)). Furthermore, both B.sub.1 and B.sub.2 bradykinin receptor activities were detected when MRNA from the human fibroblast cell line WI-38 was injected into Xenopus laevis oocytes (E. Phillips, M. J. Conder, S. Bevan, P. McIntyre, M. Webb, Journal of Neurochemistry 58, 243-249 (1992). The similarity of ligands for the two bradykinin receptor subtypes suggests a similarity between the B.sub.1 and B.sub.2 receptor genes. However, the results of genomic Southern analyses indicated that these two receptors are not highly homologous (A. E. McEachern, et al., supra; J. F. Hess, et al., Molecular Pharmacology 45, 1-8 (1994). Therefore, in order to clone the human B.sub.1 receptor, we pursued an expression cloning strategy in Xenopus oocytes utilizing the photoprotein aequorin as an indicator of Ca.sup.2+ mobilization (K. Sandberg, A. J. Markwick, D. P. Trinh, K. J. Catt, FEBS Letters 241, 177-180 (1988); E. Giladi, E. R. Spindel, BioTechniques 10, 744-747 (1991). We isolated a cDNA clone that encodes a G-protein coupled receptor with an amino acid sequence that is 36% identical to that of the B.sub.2 bradykinin receptor. The pharmacological properties of this cloned receptor expressed in mammalian cells demonstrate that it is a B.sub.1 bradykinin receptor.